An internal combustion engine is often fitted with an auxiliary device such as a fuel injection pump for supplying pressurized fuel to fuel injectors and a supply pump for supplying pressurized fuel to a common rail in the case of a diesel engine. See JP2003-184688A and JP 11-324846A, for instance.
In the prior invention disclosed in JP 11-324846A, the cylinder head 3 is formed with an axial extension 3b at an axial end thereof, and a fuel pump 40 is attached to an axial end of the cylinder head extension in coaxial relationship with the camshaft. The free end 11f of the camshaft 11 engages a drive input end 40f of the fuel pump 40 via a shaft coupler which appears to accommodate any misalignment that may exist between the cam shaft and the drive input end of the fuel pump.
JP2003-184688A discloses a similar arrangement. In FIG. 6 of JP2003-184688A illustrating prior art, the cylinder head is provided with an axial extension that is provided with a pair of bearings 8 and 9 which rotatably support an extension 4 of the exhaust camshaft 3. The camshaft extension 4 is provided with a cam 5 in a part intermediate between the two bearings to actuate a fuel pump attached to a lateral side of the cylinder head extension. In the prior invention disclosed in FIG. 1, the cylinder head extension is provided with only one bearing, and the part of the camshaft extending beyond this bearing is formed with a cam for actuating a fuel pump which is also located on a lateral side of the cylinder head extension.
The fuel pump requires a significant input torque for the actuation thereof, and the camshaft is subjected to a significant load. Furthermore, the fuel pump has a significant weight so that the part of the cylinder head supporting the fuel pump is subjected to a significant load in addition to the reaction to the input torque applied to the fuel pump. Therefore, in the prior inventions, the cylinder head was provided with an integral axial extension for firmly supporting the bearing or bearings for supporting the camshaft extension or the shaft formed with the cam for actuating the fuel pump and coupled to the camshaft.
However, providing an axial extension to the cylinder head not only increases the overall size of the engine but also complicates the manufacturing process of the cylinder head. When the fuel pump and the bearing for the camshaft extension are supported by the cylinder head via a separate member which may extend axially beyond the axial end of the cylinder head, some difficulty arises in maintaining the separate member to be firmly attached to the cylinder head. If a gap is created in the interface between the separate member and the cylinder head, the bearing for the camshaft extension may be subjected to an undue loading which could lead to a premature wear of the bearing or the journal of the extension supported by the bearing. Also, such a loading could cause vibrations and noises.
When the fuel pump is provided with a plunger as a drive input member for the actuation thereof by a cam formed on the camshaft or the extension thereof, the cam that is formed on the camshaft or the extension thereof is required to be lubricated at the surface engaging the plunger. Also, the plunger is required to be lubricated with respect to a plunger guide hole which is provided in the housing of the fuel pump. The camshaft is typically provided with an axial oil passage, but a special arrangement is required to feed the lubricating oil from the axial passage of the camshaft to the fuel pump.
JP2005-113731 discloses an invention where an extension of a camshaft extends in the manner of a cantilever from an axial end of the cylinder head, and is provided with a cam for actuating the plunger of a fuel pump. The housing of the fuel pump is directly attached to an axial end of the cylinder head. The bearing adjacent to the camshaft extension is lubricated by the lubricating oil supplied from the axial passage of the camshaft, and the lubricating oil released from this bearing is sprayed onto the surface of the cam that actuates the plunger of the cylinder head.
However, only a part of the lubricating oil sprayed from an opening in the bearing would be able to reach the surface of the cam for actuating the fuel pump, and the efficiency of lubrication may not be very high. In particular, the lubricating oil is directed to a side face of the cam, and the peripheral surface of the cam which requires lubrication may not receive any significant amount of lubricating oil. Also, no arrangement is made for the lubrication of the plunger with respect to the plunger guide hole.
In the cylinder head of an engine, a blow-by gas passage is often internally formed so that the need for external piping may be avoided. However, when a fuel pump is incorporated in the cylinder head, there may be some difficulty in forming an internal blow-by gas passage without interfering with the presence of the fuel pump.